This invention relates to electric rotating machines, and more particularly, to a new and improved brushless DC motor.
In conventional brushless DC motors, a permanent magnet rotor assembly is provided. A stator, including coils and associated electrical circuitry, is fixedly arranged within the rotor to interact with the latter and impact a rotational torque thereto. Certain problems arise, however, in motors of this type. For example, normal brushless DC motors operate from a DC supply which controls the current in phases by chopping the voltage. To achieve very high speeds, it is necessary to quickly change the direction of the current in phases. The speed achieved, however, is limited by the inductivity of the winding and the supply voltage. As such, a motor having a very low inductivity is advantageous.
Additionally, in the past, one phase permanent magnet motors with skewed stators have been utilized. Furthermore, it is well known that a two phase motor of the same size has more power than a one phase motor, and likewise, a three phase motor has more power than a two phase motor. This result will occur if the motor operates at low speed, and rotates in both directions at high starting torques. It is desirable, however, in some applications where high starting torques are not necessary, that the motor operate at high speeds, high power but rotate in only one direction. A typical application requiring these criteria is a vacuum cleaner motor. As such, for these applications, it is desirable to provide a motor which generates high power at high speeds and rotates in only one direction but does not necessarily require a high starting torque.
Furthermore, in prior high speed motors, it is extremely difficult to securely retain the magnets in their proper position without "flying off" the core. Such a problem inherently reduces the efficiency of the motor.
The present invention is directed toward solving these problems and provides a workable and economical solution to them.